Disk contacts and flat annular shield arrangement in gas filled switch



1969 c L SHACKELFORD 3,446,927

LAT ANNULAR SHIELD ARRANGEMENT DISK CONTACTS Aim IF IN GAS FILLED SWITCHFiled Jan. 10, 1966 1 1. I I 40 49 71 27 -gal- 4? Z/ 26 ,1

INVENTOR fehaarLf/am aroep ATTORNEYS United States Patent DISK CONTACTSAND FLAT ANNULAR SHIELD ARRANGEMENT IN GAS FILLED SWITCH Charles L.Shackelford, Cedar Grove, N.J., assignor, by mesne assignments, toWagner Electric Corporation, South Bend, Ind., a corporation of DelawareFiled Jan. 10, 1966, Ser. No. 519,589 Int. Cl. H01h 9/30, 33/14 US. Cl.200-144 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates toimprovement-s in gas filled switches for breaking large alternatingcurrents. The invention has particular reference to a switch forbreaking currents with a minimum amplitude of transient disturbances.

When an ordinary knife switch is opened in air while carrying a largecurrent, an arc is formed which causes erosion of the switch elementsand produces a transient disturbance in the connected electrical systemwhich may produce large resonant voltages and cause considerable damage.An improvement of the knife switch in air resides in a switch within anenclosure which is evacuated. Such an arrangement has been used but thecurrent forms a metallic vapor arc and is often cut off too abruptly andthe transients are even larger than those produced by a switch in air.The present invention is an enclosed switch provided with a shieldingmeans which insures that there will be no spark over after the switchhas been opened. The enclosure is gas-tight and contains a gas at a lowpressure. The pressure of the gas within this enclosure is maintained bya titanium hydride reservoir with lead-in connectors and a heater formaintaining the temperature of the regulator at a predetermined value.Under these conditions, when the switch is opened, an arc is formedwhich reduces the current slowly until the alternating currentapproaches a zero value at the end of a half wave. This type of currentreduction produces a transient wave which is low in current amplitudeand does not cause any damage.

One of the objects of this invent-ion is to provide an improved switchwhich avoids one or more of the disadvantages and limitations of priorart switches.

Another object of the invention is to break a large current slowly butwithin the time duration of one-half cycle of the alternating current.

Another object of the invention is to reduce the transient currentamplitude caused by a fast disruption of current flow.

3,446,927 Patented May 27, 1969 Another object of the invention is toprevent arc-over currents by providing a shielding means which reducesthe electric field intensities when the switch is in its open position.

Another objection of the invention is to maintain the pressure withinthe switching unit at a constant predetermined value.

The invention comprises a gas-filled switch for breaking largealternating currents and includes a sealed envelope for housing all theswitch components in hydrogen at a predetermined pressure. A stationarycont-act disk is conected to a lead-in conductor for forming one ofswitch contacts. A movable contact disk forms the other switch contactand is connected to another lead-in conductor. The movable contact diskis connected to flexible leads within the envelope and is secured to anexpandable bellows for sealing the envelope. The movable contact disk issurrounded by an annular shield for reducing the electrical fieldintensity at the edge of the disk.

One feature of the invention includes a filling of hydrogen gas at apressure which is below the pressure which support-s sustainedelectrical conduction.

Another feature of the invention includes the use of a hydrogen gasreservoir which may be constructed of titanium metal and its hydride.This reservoir also contains a heater with leads which may be connectedto an external source of electrical power and acts as a regulator tomaintain the hydrogen in the envelope at a predetermined pressure.

For a better understanding of the present invention, together with otherand further objcts thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

FIG. 1 is a cross sectional view taken along line 1-1 of FIG. 4 andshows all of the internal components in the switch envelope except thehydrogen reservoir.

FIG. 2 is a cross sectional view of the switch shown FIG. 1 and is takenalong line 22 of that figure. FIG. 3 is another cross sectional view ofthe switch shown in FIG. 1 and is taken along line 33 of that figure.

FIG. 4 is an end view of the switch.

FIG. 5 is a graph commonly known as Paschens curve and is plotted withvalues of volts and spacing times pressure.

Referring now to FIGS. 1 through 4, the gas-filled switch includes twoconductive panels 10 and 11 which also serve as the switch terminals.Each panel contains several mounting holes 13 for securing the panels tosome form of non-conductive mounting means or to buss bars. Connectionsfrom the panels 10 and 11 may be made by means of wire terminals 14 and15, each secured to one of the panels by bolts 16 and 17. Other means ofconnection may be used.

The switch elements are disposed within an envelope which includes ahollow cylindrical insulator 18 which may be made of either glass orceramic. The ends of the insulator are brazed to annular conductivemembers 20 and 21 and these members are Welded respectively to an enddisk 22 at one end and a conductive washer 23 at the other end. Endpieces 22 and 23 are soldered or welded to terminal portions 24 and 25,these portions containing threaded holes for accommodating a pluralityof machine screws 26 which anchor the switch envelope to the two endpanels 10 and 11.

The cylindrical insulator 18 may be formed in a single cylindrical piecebut it has been found that better shielding means may be obtained by theinstallation of a floating electrode shield 27 This shield may have anannular flange 28 which separates the cylindrical insulator into twoportions. While the shield 27 is generally left floating and therebyassumes a voltage which lies somewhere between the potentials of the twoend portions, some applications may require connection of flange 28 to avoltage divider connected between the two end panels or to some otherpotential.

Inside the envelope a contact disk 30 is supported on another disk 31,the edges of which are turned over to provide an annular shield 32.These two elements 3 and 31 are also secured to a heavier piece of metal33 which may be made of copper and which acts as a heat sink. This arrayof electrodes is supported on a hollow metal cylinder 34 which in turnis secured to conductive panels 22 and 24. Cylinder 34 is provided withseveral holes 35 so that the gas in the envelope may move through themwhen the envelope is exhausted. A tubular conduit 36 is welded to disk22 and is used as an exhausting and filling means. It is sealed bycrimping in the well known manner and is protected by a cap 37 whichsurrounds the end of conduit 36 and which is secured to end panel 10.Current is lead into the interior of the envelope by means of clampingscrews 26, disks 24 and 25, conductive members 20 and 21, and conductivecylinders 34 and 44.

The other contact member is a movable disk 40 secured to a cylindricalpiece of copper 41 which acts as a conductive element and a heat sink.Secured to the cylinder 41 are four flexible leads 42 which carry thecurrent from cylinder 41 and disk 40 to another washer 43 secured to astationary cylindrical conductor 44. Conductor 44 surrounds a bellows 45and is secured to conductive washer 23 and supporting means 25. Washer23 is connected directly to end panel 11 by four screws 26.

The flexible leads 42 are composed of a plurality of fine copper wireswhich may be braided or otherwise joined to form a conductive andflexible current carrying means. The stationary ends of these conductorsare soldered to tubes 46 which are an integral part of a washer 47 andring 43. The washer 47 is welded to the inner end of the bellows 45while the outer end of the bellows is welded to another washer 48,secured to an axial rod 50. Washer 47 is also connected to a cylindricalconductive shield 49 lying within shield 47. Rod 50 is connected tocylinder 41 by any conventional means such as a screw thread and inaddition is connected to an exterior rod 51 which may be coupled to ahandle for manual operation or to a circuit breaker actuating mechanismwhich separates contact portions 30 and 40 whenever certain conditionsarise which call for the opening of the switch.

FIG. 2 shows a hydrogen reservoir 52 having lead-in conductors 53 and54. These lead-in conductors pass through washer 23 and the annularsupport 25 so that an electrical source of power may be connected tothem and heat up the reservoir to a predetermined temperature. Only onelead-in conductor is necessary, the other heater terminal may beconnected to washer 23. The reservoir 52 may be made of many materialsbut it has been found that a cylinder of titanium is the most efficientreservoir material. As is well known, the titanium metal combines withhydrogen to form titanium hydride, the extent of such combination beingdependent upon the temperature of the reservoir. By applying the rightamount of heat to the reservoir, a definite pressure of hydrogen may bemaintained within the envelope. Other isotopes of hydrogen such asdeuterium or tritium may be used, these forms having different Paschencurves.

FIG. is a graph showing the Paschen curve for conduction within anevacuated envelope. This curve is well known and has been described andillustrated in many .4 publications. The curve 56 r epresents a mirrorvalues of voltage and electrode spacing times gas pressure where a sparkstarts without benefit of prior gas ionization.

The operation of this device is as follows: let it be assumed that disk40 is in contact with disk 30. This permits current to pass fromconnector 14 to connector 15 with substantially no loss of power. Atthis time the reservoir 52 is heated to a temperature which provideshydrogen at a predetermined low pressure in the envelope. Now let it beassumed that the switch is to be opened for any reason. Rod 51 is movedto the position shown in FIG. 1 and disk 40 is moved away from disk 30.An arc is formed between the two disks but because of the low pressurewithin the envelope there is a minimum of sputtering and the electrodesare not damaged. The two disks 30 and 40 are separated by an amountindicated by the distance 57. When the contacts are separated, thecondition is represented by the arrow 58 which moves from a zero spacingcondition to a point 60 where the arc is extinguished. If the switch isopened at a time when the voltage of the AC. power has a substantialpositive or negative value, an arc is formed which continues until thevoltage reaches a zero value between positive and negative waves. Atthis time the arc is extinguished and cannot be re-formed because point60 is in the non-conducting area.

The above described action may take several milliseconds or theexistence of the are between disks 30 and 40 may be quite short. In anyevent, the arc is extinguished when the current wave passes through zeroand, because of this, the transient wave set-up, due to the disruptionof current, has a minimum amplitude.

After the switch has been opened and the transient wave has disappeared,the two conductive end portions 10 and 11 are insulated from each otherby the hollow insulator cylinder 18. The tendency to are over betweenthese two contact portions 30 and 40 is reduced by an annular washertype shield 61 which lies flush with the surface of the movableelectrode 40 when the switch is in its opened position. Washer 61 isconnected to electrode 40 by means of shield 49 and washer 47 and theelectric field between washer 61 and electrode 30 is the same as thefield between electrodes 40 and 30. However, there are no sharp pointsnor corners to intensify the-electric field and, in addition, thefloating electrode 27 divides the electric field into two equal parts inthe annular space surrounding the switch components.

It should be noted that there are two gas pressures within a largevoltage range wherein the combination of voltage and electrode spacinglie in a non-conductive region. It has been found that operating in theregion indicated in FIG. 5 produces the best results. There is no largeare when passing through the conductive region and the arc can besuppressed much faster.

The foregoing disclosure and drawings are merely illustrative of theprinciples of this invention and are not to be interpreted in a limitingsense. The only limitations are to be determined from the scope of theappended claims.

I claim:

1. A gas filled switch for breaking alternating currents comprising; asealed envelope for housing all the switch components in a gas atreduced pressure; said envelope containing a stationary contact diskconnected to a leadin conductor for forming a stationary switch contact,a movable contact disk connected to a lead-in conductor for formingamovable switch contact, said movable disk connected to flexible leadswithin the envelope and to an expandable bellows for sealing theinterior of the envelope from the atmosphere a flat annular shieldsurrounding said movable contact disk for reducing the electrical fieldintensity, said annular shield mounted coplanar with the contact surfaceof the movable disk when in its open position, said gas pressure lessthan the pressure necessary to produce conduction at the voltage andspacing between the contacts when open but large enough to support atemporary are when the disks are being separated.

3,446,927 5 6 2. A switch as claimed in claim 1 wherein the station-References Cited ary disk and the annular shield are each connectedrespectively to cylindrical conductive shields positioned in UNITEDSTATES PATENTS axial alignment with the disks. 92,912 6/ 1959 Greenwoodet al.

3. A switch as claimed in claim 1 wherein the envelope 3,156,803 11/1964Scully et al.

contains a titanium reservoir for maintaining the gas pres- 5 3,189,7156/ 1965 Jennings.

sure in the envelope at a value where sustained gaseous 3,261,954 7/1966Yonkers.

conduction is impossible at the spacing between the open 3,328,545 6/1967 Holliday.

disks.

4. A switch as claimed in claim 1 wherein the gas in ROBERT S, MACON,Primary Examiner. the envelope is selected from the group whichconsistsof 10 hydrogen, deuterium, and tritium.

